With an increase of requirements on environmental protection, oil standards are increasingly higher. Newly formulated gasoline is required to satisfy the requirements such as high octane number, ultralow sulfur content, low alkene content and low aromatic hydrocarbon content. An alkylation process is a process of enabling light alkene to react with isobutane to produce an alkylated product containing rich isooctane. This alkylated product, almost all components of which are high-octane-number isoalkane, does not contain unideal components such as sulfur, alkene and aromatic hydrocarbon and is an ideal component of newly formulated gasoline.
Almost all alkylated oil is prepared by enabling isobutane and butene to react in condition of existence of an acidic catalyst. Sulfuric acid is one of major catalysts for alkylation reaction. However, the solubility of alkene and isoalkane which are the alkylation reaction raw materials in the catalyst, i.e. concentrated sulfuric acid is poor. Particularly, isobutane is very difficult to be dissolved in concentrated sulfuric acid. However, alkylation reaction is a quick reaction process. Therefore, full mixing of acid and hydrocarbon phases has a significant influence on product quality. Besides, although the solubility of alkene in concentrated sulfuric acid is slightly better than that of isobutane, alkene is very easily polymerized at temperature above 10° C. to produce polymers above C12. Besides, alkylation reaction is an exothermic reaction. If the reaction temperature is not properly controlled, the side reaction of alkene polymerization will be intensified. Therefore, temperature is also one of decisive variables in alkylation reaction. The lower the temperature is, the smaller the trend of the side reaction of alkene self-polymerization or reaction with acid to produce alkyl sulfate is. When the reaction is performed at lower temperature, a better conversion rate can be achieved and a high-quality alkylated product can be obtained. Therefore, the sulfuric acid alkylation process not only needs to realize full mixing of acid and hydrocarbon phases, but also needs to guarantee that alkylation reaction is performed at low temperature.
At present, a reactor adopted in the sulfuric acid alkylation process is a STRATCO reactor, in which a great number of tubular heat exchangers are disposed and materials are, by a mixing impeller, forced to circulate in mass so as to achieve reinforced mixing and heat transfer. Besides, it is beneficial to the quality of the alkylated product to increase a ratio of isobutane to alkene in the reactor, and a ratio of alkane to alkene and a ratio of acid to hydrocarbon in a reaction area can be improved through mass circulation of materials. However, since the viscosity of materials increases with the decrease of temperature, the difficulty in circulating the materials through the mixing impeller increases rapidly with the drop of the temperature of a reaction system, such that the system can be operated only at temperature above 0° C., and specifically at temperature above 4° C.
Therefore, there is a demand in industry for new high-efficiency processing methods and systems used for alkylating isoalkane.